The application of thin films through vapor deposition is an important manufacturing process in a wide variety of industries, including semiconductor manufacturing, glass coating, the manufacture of compact discs (CDs), decorative coatings, and the manufacture of flat panel displays. In chemical vapor deposition (CVD), a substrate is exposed to one or more chemical precursors, which react with or decompose on the substrate to form the desired film. In physical vapor deposition (PVD), the thin film is deposited on the substrate through physical rather than chemical means. Examples of PVD include evaporation, sputtering, and radio-frequency (RF) plasma processes.
In a sputtering process, for example, electrical energy is used to ionize a gas within an evacuated coating chamber, generating a “plasma.” The positively charged ions of the plasma bombard a material called the “target,” causing atoms of the target to be knocked free. The majority of these atoms are electrically neutral ions that “drift” from the target to the substrate, where they condense or react with the substrate to form a thin film on the substrate. Common sputtering targets include aluminum, boron, copper, iron, nickel, silver, titanium, and zinc.
Contamination of the target is a significant problem in plasma-based deposition processes. A target may become contaminated in a variety of ways. For example, the surface of the target may become oxidized or contaminated before it is placed in the chamber by exposure to air, water vapor, or airborne hydrocarbons. A target may also become contaminated during the vapor deposition process. Some of the sputtered material may be re-deposited onto surfaces outside the target erosion area or “racetrack.” This re-deposited material has a different structure from the target material and can lead to electrical arcing on the surface of the target. Arcing can affect the quality of the deposited film by introducing particulate matter into the film. Yet another source of contamination is an arc in the so-called “cathode dark space” (the physical space between the target—the negative-potential element in many applications—and ground). When such an arc occurs, deposition is severely affected, and damage to the target or the substrate may result in addition to the contamination of the target, the substrate, or both.
There are a variety of methods for conditioning or removing impurities from a target. For example, the target may be physically (i.e., manually) cleaned. Another approach is to operate the sputtering process with the contaminated target for a period sufficient to “burn off” the impurities. In this approach, the substrate may be omitted from the chamber, or “dummy” substrates or actual substrates that are simply discarded may be used. A different approach involves blasting the surface of the target with a finely divided powder having a particular range of particle diameters. An alternative method involves using reverse bias pulses to perform target conditioning while eliminating arcing entirely.
Conventional methods for conditioning a vapor deposition target often require significant time (e.g., several hours) to complete, the venting of the vacuum chamber and the removal of the target, or both. It is thus apparent that there is a need in the art for an improved method and system for conditioning a vapor deposition target.